1. Field of the invention
The present invention relates to a picture information memory device and a picture information reproducing device, and more particularly, to a picture information memory device using a Pockels Readout Optical Modulator (PROM) element and capable of selectively and optically recording picture information which repeatedly appears at a regular period, and to a picture information reproducing device for reproducing the picture information recorded in the picture information memory device.
2. Description of the Related Art
Various picture information memory devices, such as a camera tube, a two-dimensional CCD array, have heretofore been put to practical use. In such devices, light from an object to be recorded is converted into electric signals to record and reproduce a picture of the object.
There is a strong demand for selectively, from the entire incident image, recording an image produced from the light which repeatedly appears at a regular period, e.g., an image produced from light emitted and flashed at the regular period. For example, there is a strong demand for development of picture information memory devices capable of clearly recording spark discharge patterns which occur at an insulator connecting portion and a transformer both employed in a high-voltage transmission line. In picture information memory devices which are now put to practical use, however, the entire light incident on a photoelectric converter portion, are photoelectrically converted, and therefore both the light produced by a spark discharge and the light from the background are photoelectrically converted. Therefore, an image produced by the spark discharge are superimposed on a background image, thereby making it impossible to clearly record only the image produced by the spark discharge.
A PROM element of a spatial light modulator, has already been known as a picture information memory device. Here, the PROM element is defined as an element which generates electric charges corresponding to the intensity of write-in light incident thereon due to an photoconductive effect, holds the generated electric charges as polarized charges, and varies the polarization state of readout light incident thereon according to the polarized charges due to the Pockels effect. The PROM element includes, for example, a Bi.sub.12 SiO.sub.20 single crystal plate. Picture information is written into the PROM element by using a photoconductive effect, and the picture information is read therefrom by using the Pockels effect.
That is, in writing the picture information into the PROM element, the PROM element is irradiated with write-in light with a direct-current bias voltage being applied to the PROM element, thereby forming polarized charges corresponding to the picture information inside the PROM element so as to record the picture information therein. When the recorded picture information is read, linearly polarized light is projected onto the PROM element under a direct-current biased state or a non-biased state, thereby reading the picture information from the PROM element by making use of the Pockels effect based on the polarized charges formed inside the PROM element. When a picture information memory and reproducing device using the PROM element is used, an incoherent optical image can be converted into a coherent optical image, and the optical image can be subjected to an optical Fourier conversion. Thus, various advantages can be achieved in an image analysis.
When the above-described PROM element is used as a picture information recording medium, various optical image information processings can be effected to the recorded image. Thus, if only a picture repeatedly appearing at a specific frequency, of various incident pictures, can be recorded in the PROM element, various advantages in terms of the image analysis can be achieved as well as the recording of a periodically-appearing picture in the PROM element.
In the conventional picture information memory device for recording the picture information in the PROM element, however, both a background image and an image appearing at a regular period are recorded in the PROM element in a superimposed state. It is, therefore, impossible to selectively record the image appearing repeatedly at a regular period. As a result, the periodic image cannot be selectively and clearly recorded and reproduced.